1. Field of the Invention
This invention relates to an ignition timing controlling apparatus of an internal combustion engine, especially to ignition timing controlling apparatus which is improved in starting characteristic of the internal combustion engine.
2. Description of Related Art
FIG. 1 is a block diagram showing a construction of a conventional ignition timing controlling apparatus. In the figure, reference numeral 5 is a load sensor such as a boost sensor or the like which detects boost pressure of the inside of the intake manifold of an engine. The load sensor 5 detects load of the engine. The load sensor 5 is connected to an input interface (hereinafter to be called as input I/F) 6 together with a rotation sensor 4 which detects the number of the rotations of a crank shaft (or a cam shaft) of the engine and the referential position of a rotational angle thereof (hereinafter to be called as a crank angle). The input I/F 6 is connected to a microprocessor unit (hereinafter to be called MPU) 7 through a bus. Still more, the MPU 7 is connected to a ROM 8 which stores target ignition timing data and the like wherein control program, the number of rotations and load are made to be set as parammeters, to a RAM 9 which stores various kinds of control information, and to an output interface (hereinafter to be called as output I/F) 10. The MPU 7 reads out the target ignition timing data stored in the ROM 8 as parameters being the number of rotations and load, and calculates the target ignition timing on the basis of the read out target ignition timing data. The MPU 7 calculates the detected period according to the referential position of the crank angle detected at the rotation sensor 4, and calculates the time required for ignition from the referential position on the basis of the calculated period, detected referential position and calculated target ignition timing. When the rotation sensor 4 detects the referential position, the MPU 7 outputs an ignition control signal which instructs the ignition of the engine to the output I/F 10 through a bus after the calculated time has passed. An ignition control unit 11 is constituted by above mentioned input I/F 6, MPU 7, ROM 8, RAM 9 and output I/F 10.
The output I/F 10 is connected to a base of an ignition unit 12 employing an emitter-grounded transistor. The collector of the ignition unit 12 is connected to one end of the primary coil of an ignition coil 13. One end of the secondary coil of the ignition coil 13 is connected to an ignition plug (not shown). The ignition unit 12 switches on/off the electric current to the primary coil with the use of the ignition control signal. The other end of the primary coil is batch-connected to the other end of the secondary coil and one end of an ignition switch 14. The one end of the ignition switch 14 is also connected to the ignition control unit 11. The other end of the ignition switch 14 is connected to positive electrode of a battery 16 whose negative electrode is grounded. The ignition switch 14 switches on/off the electric current supplied from the battery 16. And the positive electrode of the battery 16 is connected to one end of a control relay 15 whose other end is connected to the ignition control unit 11. The control relay 15 is used for backing up the electric source of the ignition control unit 11. When electric source voltage V.sub.B is given to the ignition control unit 11 through the ignition switch 14, a control signal is given to the control relay 15 from the MPU 7 through the output I/F 10, thereby the control relay 15 is on. When the ignition switch 14 is off, and the MPU 7 completes the predetermined calculation, the control relay 15 is off by the control signal indicating the completion thereof. In other words, at the time when the ignition switch 14 is off, the MPU 7 sometimes has not yet completed the internal operation. Accordingly, the MPU 7 is required to be supplied electric source voltage V.sub.B until it completes the internal operation, and that is why the control relay 15 is provided.
FIG. 2 is a drawing showing operational waveforms of respective parts of the ignition timing controlling appartus shown in FIG. 1. In addition, in order to explain simply, the case where the ignition control signal is outputted in synchronism with the detected signal of the rotation sensor 4 is taken as an example here.
The conventional ignition timing controlling apparatus of the internal combustion engine is constituted as the above. When the ignition switch 14 is on at the time of starting, the electric source voltage V.sub.B from the battery 16 is supplied to the ignition control unit 11 through the ignition switch 14, following the route indicated by "a" in FIG. 1 which passes the ignition switch 14. After the electric source voltage V.sub.B being supplied, the MPU 7 makes the control relay 15 operate and supplies the electric source voltage V.sub.B to the ignition control unit 11, following the route indicated by "b". Accordingly, once the ignition switch 14 is on, the supply of the electric source voltage V.sub.B is to be continued by the control relay 15 even when the ignition switch is off thereafter. In this way, the electric source supply to the ignition control unit 11 is backed up.
An ignition control signal as shown in FIG. 2(b) is outputted in synchronism with the detecting signal of the rotation sensor 4 shown in FIG. 2(a). At the leading edge of the above mentioned ignition control signal, high voltage is generated at the secondary coil, thereby, ignition of the engine is carried out. The leading edge of aforesaid detecting signal becomes the referential position of the crank angle. The electric source voltage V.sub.B is supplied to the ignition control unit 11 through the control relay 15 and the electric source is supplied to the rotation sensor 4 from the ignition control unit 11, even if the ignition switch 14 is off when the detecting signal is "H" level at the time of T.sub.1, thereby the engine being stopped. Therefore, the output signal of the rotation sensor 4 is continued to be outputted at "H" level as it is, and the ignition control signal in FIG. 2(b) stops with the ignition coil 13 being in the close state. Hereupon if the ignition coil 13 is continued to be on, the problem is created that the ignition coil will be burning and so on. So a control for shutting off supplying electric current to the ignition coil 13 is carried out after the time t has passed since the start of the supply. When the ignition switch 14 is on again at the time T.sub.2, that is, before shutting off supplying electric current, the ignition control signal changes to "L" level at the time T.sub.3 after time t has passed since the start of the supply, thereby ignition of the engine is carried out at the ignition timing T.sub.3 whose rotational angle advances more than the ignition timing T.sub.4 which originally is the timing to be desirably ignited.
The ignition timing controlling apparatus of the internal combustion engine as afore described has a problem that the engine starts earlier than desired when the ignition switch 14 is on again to start the engine at the time of engine stop due to the open-state of the ignition switch 14.